a) Field of the Invention
The invention concerns a cordless electric appliance. In particular, the present invention concerns a cordless electric screwdriver which includes provisions for plugging the screwdriver directly into a standard electrical power socket.
b) Description of Related Art
Conventional electric screwdrivers are either of the "corded" or the "cordless" variety. Corded electric screwdrivers are electrically linked to a power source socket by finite length wire conductors. By convention, the electrical contact tangs of a male plug-in connector are associated with an electrical appliance, and each tang is respectively received in a female electrical contact of a power source socket. Also by convention, the electrical contact tangs and female electrical contacts are arranged in a standardized pattern to facilitate mating between the plug and socket. A disadvantage of corded screwdrivers is the range of operation is limited to the finite length of the wire conductors from the power source socket. Another disadvantage is the added bulk and inconvenience a cord causes in tight spaces.
Conventional cordless electric screwdrivers include an internal power reserve. The internal power reserve may be provided by standard, non-rechargeable batteries, however the most common power reserve is one or more rechargeable batteries. During periods of screwdriver inactivity, the rechargeable batteries may be linked to a power source socket through a recharging unit.
Known recharging units for cordless electric screwdrivers generally consist of either a rectifying transformer unit which is simultaneously "plugged-in" between both a standard electrical power source socket and an input receptacle on the screwdriver, or a support bracket which cradles the screwdriver and concurrently establishes electrical links between the bracket and the screwdriver. Consequently, it is necessary to have either the rectifying transformer unit or the support bracket to recharge the screwdriver.
Inasmuch as it is not always convenient to carry an additional rectifying transformer unit or support bracket for recharging the cordless electric screwdriver, having a separate, secondary element becomes a disadvantage.